Technology and Innovation

DEPTH OF FOCUS — The range through which the image plane (the emulsion of the film) can be moved backward and forward with respect to the camera lens such as defined under the depth of field and circle of confusion. This term is often confused with depth of field and vice versa.
In common English. Depth of Field is what the photographer is interested in; it is what is in acceptable focus in front of the lens. Depth of Focus is what only a technician is interested in; it is what is in focus behind the rear lens element which the film or image sensor “sees.” Kerry Lee

I was surprised to see the misstated comments on Depth of Field vs. Depth of Focus in the June 2007 Your Tips get past your editors. To clear things up. here are the definitions of the two phrases from The American Cinematographer Manual (4th edition, 1973, page 625).
• DEPTH OF FIELD — The range of object distance within which objects are in satisfactory sharp focus, the limits being the establishment of a circle of confusion of greatest acceptable size.